This invention relates to semiconductor devices and the manufacture thereof and, in particular, to semiconductor devices including silicides.
Polysilicon has conventionally been employed for gates and interconnections in integrated circuits. However, for small geometry, high speed integrated circuits it is desirable to use alternative materials with lower resistivity, such as metallic silicides. Our co-pending GB Applications No. 8328552 (Ser. No. 2139420) (P. D. Scovell et al 5-3-2X) and No. 8312281 (Ser. No. 2139419 (P. D. Scovell et al 7-4-3) describe methods of forming metallic silicide elements.
Titanium disilicide is now one of the most favoured replacements for heavily-doped polysilicon as an interconnect in MOS devices with geometries down to 1 .mu.m. Titanium disilicide has numerous beneficial qualities. It is a refractory metal. It has the lowest thin film resistivity of any refractory silicide. It is readily etched. Metal over the silicide can be etched with great selectivity, and a high quality silicon dioxide layer can be grown over the silicide with no chance of forming volatile metal oxides. One significant disadvantage of this material is that it does not form a barrier to silicon diffusion from beneath the silicide. Thus where aluminium is disposed over silicide, silicon can diffuse up into the aluminium where it can precipitate to form a high resistance layer, and this diffusion is a significant cause of device failure. It is an object of the present invention to overcome this disadvantage.